Coating compositions



ou ETAL 3,419,406

COATING COMPOSITIONS Filed Aug. 4, 1967 SENSITIVE sue/1.1250 01.420RES/N FHYDROPH/L/C LAYER Dec.3l,1968 J.

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' m 1 2 F2 F2 a GRA/NED ALUMINUM EXPOSED STABILIZED D/AZO RESINHYOROPHlL/C LAYER ERA/NED ALUMINUM JAAIES E HOUL E GIL DEN 8RMAN VAN NINVENT RS A TTORNEY 8, AGENT United States Patent 5 Claims. (Cl.106-287) ABSTRACT OF THE DISCLOSURE Aqueous solutions of complexes oftitanium compounds render substrates hydrophilic, for example, asolution resulting from the addition of hydrogen peroxide, phosphoricacid and tetraisopropyl titanate to water when coated on an aluminumsupport renders the support hydrophilic.

This is a continuation-in-part application of US. Ser. No. 347,931 filedFeb. 27, 1964, by James F. Houle and Gilden R. VanNorman, now US. Patent3,342,601.

This invention relates to lithographic printing plates, moreparticularly to offset printing plates commonly used in the lithographictrade.

Lithographic plates are well known in the graphic arts field,particularly those having metal supports such as aluminum or zinc. Inrecent years aluminum has been particularly attractive for lithographicplates due to its cost, availability and light weight. However, whenaluminum is used as a substrate for printing plates, certain inherentdisadvantages must first be overcome. For instances, it has beenestablished that the naturally occurring oxide film on aluminum is notsufficiently hydrophilic to provide trouble-free operation on alithographic printing press. The bare aluminum is prone to becomeslightly hydrophobic or oleophilic resulting in a gradual buildup of inkon the nonprinting areas. This phenomena is referred to in the trade astoning or scumming. -In order to eliminate toning or scumming, asuitable, permanently hydrophilic surface which is relatively insolublemust be provided. Aluminum is also known to react with certain sensitivematerials, such as diazo resins coated thereon, as indicated in US.Patent 2,714,066.

Several mehods of imparting an insoluble, permanently hydrophlic surfaceto the aluminum substrate have been suggested in the prior art. Typicaltreatments include anodizing, coating the surface with a hydrophilicorganic polymer, etc. For instance, a method is described in FrenchPatent 904,255, published Oct. 31, 1945, showing chemical or electricaltreatments which provide a porous layer of aluminum compounds of oxygen,fluorine or phosphorous. In addition, Clerc, in the Ilford Manual ofProcess Work, 1946, page 237, discloses treatment of aluminum plateswith solutions containing fluosilicic acid or a fluosilicate.

These treatments, however, have not been satisfactory in producing asuitable hydrophilic coating on the aluminum adequate to provide therequired ink-water differential for successful operation on alithographic press. Moreover, the above treatments do not protectconventional diazo coatings from the aluminum so that the plates can bepresensitized and stored over long periods of time prior to usage.

One method of providing an aluminum plate having an insoluble,hydrophilic layer which also isolates the diazo light sensitive coatingfrom the aluminum substrate is to deposit a coating on the aluminum of asilicate containing the Si0 radical.

Patented Dec. 31, 1968 A presensitized aluminum lithographic platehaving a silicate layer thereon, has limited press life and also issubject to decreases in sensitivity during storage, especially after theplate has been exposed to the atmosphere particularly with high humidityor heat or a combination of both. Therefore, it has been desirable toprovide a plate having greater press latitude, longer press life andlonger shelf life than provided by the plates of the prior art.

Coating an aluminum surface with silica or similar silicate undercoatingrequires a smooth aluminum surface. However, it has customarily beenfound in lithographic printing that a grained or brushed surfaceprovides a wider set of operating conditions on the press, particularlysince a grained plate requires a less critical ink-water balance thandoes the silicate coated smooth plate. Moreover, the less criticalink-water balance decreases the tendency for the ink to emulsify duringmulticolor printing, which normally results in a loss of imagesharpness. Therefore, it has also been desirable to provide apresensitized aluminum plate having a grained or brushed surface.

In order to provide an insoluble hydrophlic surface or surface coatingit is desirable to eliminate the necessity of elevated temperatures andsubsequent Washing during the process. These steps are essential in manyof the known processes. It is also desirable that the treatment beconducted from aqueous media thus eliminating toxic or flammable solventvapors. Therefore, to achieve improved characteristics for apresensitized plate, it is desirable to obtain a plate having a grainedsurface, an improved method of treatment to provide a hydrophilicsurface and a stablized light sensitive coating thereon, thus giving acombination of superior printing and keeping qualities.

We have found that a suitable insoluble, hydrophilic surface layer maybe imparted to an aluminum sheet by treatment with aqueous solutions ofcertain complex titanium salts capable of reacting at or on the surfaceto form an insoluble layer.

One object of this invention is to provide a hydrophilic lithographicprinting surface. Another object is to provide a coating composition fortreating surfaces such as metal, paper, polymeric, etc. to render asurface hydrophilic for use in lithographic printing. A further objectis to provide a presensitized lithographic printing plate. A stillfurther object is to provide a diazo sensitized, grained aluminum,lithographic printing plate. Another object is to provide a novelcoating composition which adheres tenaciously to various supportsincluding metals such as aluminum, zinc, copper, and the like, and topolymeric materials such as polyesters, polyamides, polystyrene,cellulose esters, etc., to provide a hydrophilic coating substantiallyfree from water-soluble materials and to which can be adhered lightsensitive coatings, printing inks, paints, etc. Other objects will beapparent from the following disclosure.

The above objects and other objects are attained by making a coatingcomposition in an acid medium of a titanium compound which issubstantially water soluble.

A useful source of titanium compound is the titanium orthoesters suchas, for example, the tetraalkyl titanates. Although other titanates maybe used, the preferred tetraalkyl titanates are those having alkylgroups with 2 to 5 carbon atoms such as, for example, tetraethyltitanate, tetrapropyl titanate, tetraisopropyl titanate, tetrabutyltitanate, tetraisobutyl titanate, tetraamyl titanate, etc.

The acidic constituent which is useful for reacting with the titanateproduces a water-soluble titanium complex in an acid media. Usefulacidic constituents include, for example, fluosilicic acid, hydrofluoricacid, phosphoric acid, fiuoboric acid, etc.

The coating composition is advantageously prepared by adding the alkyltitanate to the dilute aqueous acid,

whereupon the alkyl titanate immediately reacts to form hydrous titaniumdioxide which subsequently dissolves and/or reacts forming a hydrophilictitanium complex. When fluosilicic acid is employed to form titanylsilicofluoride, a useful molar range of fiuosilicic acid to tetraalkyltitanate is from 5:1 to 1:1 moles, although a preferred molar range isfrom 2:1 to 1:1 moles. The pH of the coating compositions may be variedfrom about 1.0 to 5.0.

A useful molar range of fluoboric acid to tetraalkyl tltanate is from7:1 to 2:1 moles.

When phosphoric acid is used as the acidic constituent, hydrogenperoxide should also be used. The resulting complex appears to betitanium peroxy phosphate. The alkyl titanate is added to a dilutehydrogen peroxide solution. When solution is complete, phosphoric acidis then added. In a preferred composition we use 6.810.7 moles hydrogenperoxide per mole alkyl titanate and 2.37 moles phosphoric acid per molealkyl titanate. It will be fully realized that the volumetricproportions may be varied and that the amount of water used is notcritical but must be suflicient to provide solubility. Hydrogen peroxidecan also be used with the other acids.

A useful coating composition is also obtained by preparing a pertitanicacid by dissolving the alkyl titanate in hydrogen peroxide.

Various methods of applying the coating may be used including directroll, immersion, hopper, knife, Wick, bead, spray or any method ofconvenience. The coating may be on one or both sides of the support.

The thickness of the titanium complex layer on an aluminum substrate isdiflicult to determine due to its thickness. However, it is most likelyin the range of thickness of the naturally occurring oxide.

Drying occurs rapidly, but in production, driers may be usedadvantageously, employing heat by known means, such as hot air, infraredlamps, etc.

The light sensitive coating may be a suitably stabilized water-solubleresin containing the diazonium group which upon exposure to ultravioletlight forms an oleophilic surface or image.

The light sensitive coating may be of the general formula.

N-N2+'X- MX2 2 z where X is Cl.

M is a dior trivalent metal of the groups known to stabilize thediazonium groups, eg cadmium, zinc, bismuth, arsenic, antimony, tin,iron, platinum, mercury.

X is an anion or mixture of anions consisting of halogen or sulfates.

Z may be a phenyl or substituted phenyl in which case the resin is analdehyde condensation product of a p-diazodiphenylamine salt. In thiscase, Y is hydrogen.

Z and Y may also be organic radicals functionally capable of enteringinto an addition polymerization, polyesterification, condensation orother reaction capable of producing a relative low molecular weightresin or capable of reacting with a preformed polymer. Z and Y in thiscase may be the same or different, the parent diazonium compound being asubstituted p-diazo aniline.

Some examples of the reactive groups are hydroxyl as inN-ethyl-N-((S-hydroxyethyl)-anilino, 4-diazo salts capable of reactingwith polymerizable groups such as aeryloyl, methacryloyl, etc.

The placement of various groups on the anilino nitrogen can result inthe preparation of polyesters, polyethers, polyurethanes, polyacetals,polycarbonates, etc., by direct polymerization or condensation withfunctionally proper preformed polymers.

In a preferred embodiment, the light sensitive coating consists of analdehyde condensation product of a p-diazo diphenyl amine. Lightsensitive aldehyde condensation products of p-diazo diphenyl aminestabilized with metal salts are well known in the art as described inUS. Patent 2,714,066. Such resins are also available commercially, e.g.Diazo Resin No. 4, supplied by Fairmount Chemical Co. This material isdescribed as a diazonium sulfatezinc chloride double salt. However, asstated in the prior art, aluminum reacts with the diazo resin causingdecomposition. Therefore, in a preferred embodiment we used a method ofpreparation and stabilization of the light sensitive diazo resins suchthat they are less sensitive to decomposition by the aluminum surface.

The presensitized, grained aluminum printing plate prepared according toour specifications, may be handled and treated in use as is customary inthe art. The unexposed areas are removed and the plate lacquered, afterwhich the plate is used on a lithographic printing press.

The sensitive layer for the lithographic plate can be exposed to visiblelight, ultraviolet light, infrared light, X-rays or to heat patterns inorder to form differential areas for printing. It is possible to uselight sensitive organic compounds such as aliphatic and aromatic esters,hydrazides and amides of napthoquinone-diazide-sulfonates,cinnamalrnalonic acids, their substitution products and functionalderivatives, diazonium salts of amino-diphenyl amines and theircondensation products with formaldehyde, orthoand paraquinone diazidesof benzals, anthracenes and heterocyclic systems, for example,quinoline, indazoles, benzimidazoles, diphenyloxides, also diazoketones,unsaturated ketones, orthoand paraiminoquinone diazides, derivatives ofalkylnitronaphthalenesulfonats, nitroaldehydes, acenaphthene, stilbene,azides and diazides and high molecular polymer diazo resins. Silverhalide emulsions may also be used. Moreover, the subbing may beovercoated with a photoconductive layer having a high electricalresistance which can be charged and subsequently discharged by light orheat as in electrophotography, for example, low or high molecular weightorganic photoconductors, also mixtures thereof with resins. Particularlysuitable as photoconductors are oxadiazoles, imidazolones, triazole,oxazole, thiazoles, hydrozones, triazines, polyvinyl carbazone andpolyvinyl oxazoles.

Useful resins may contain groups which tend to make the resins solublein alkali, such groups include acid anhydride, carbonic acid, sulfonicacid, sulfonamide and sulfonimide groups, for example, polyvinylpolymers or mixed vinyl polymers, phthalic acid ester resins, alkylresins, rosins and polyacrylic acid resins.

The lithographic plates of the invention are further characterized bygood adhesion and produce good removal of the unexposed areas so thatthey can produce a large number of copies.

The drawing shows one embodiment of our invention.

FIG. 1 shows a grained aluminum sheet 3 having thereon a. hydrophiliclayer produced by treatment with a titanyl salt complex 2 and havingthereon a light sensitive stabilized diazo resin 1.

FIG. 2 shows the structure of FIG. 1 following exposure to light andremoval of the unexposed areas of the stabilized diazo resin.

The following examples are intended to illustrate our invention but notto limit it in any way.

Example 1.Titanyl silicofiuoride' A sheet of brush-grained aluminumhaving a thickness of 5 mils is immersed in a solution of titaniumcomplex prepared by agitating vigorously a solution of 750 ml. ofdistilled Water in 50 ml. of 31.9% fluosilicic acid, while 10 ml. oftetraisopropyl titanate is added rapidly in a fine stream. The aluminumis then passed between two mechanically driven inch diameter rubberrolls under sufiicient pressure to remove the excess solution. A verythin film of solution is thus obtained which dried rapidly at roomtemperature. Similar coatings are obtained on other supports includingpolymeric material, paper, metal, etc.

Example 2.Titanyl peroxy phosphate To 740 ml. of water is added ml.(16.9 g.) of 85 percent phosphoric acid (0.1588 mol) and ml. (33 g.) of28 percent hydrogen peroxide (0.262 mol). Then with good agitation 10ml. (9.55 g.) of tetraisopropyl titanate (0.0336 11101) is added. Theresult is an orangeyellow solution which is ready for coating. Thissolution is coated as in Example 1 to give a thin coating on the surfaceof the support.

Example 3.-Preparation of a titanyl fluoborate coating solution To 750ml. of Water is added 14.7 g. (0.0672 moles) of percent fiuoboric acidwith sufficient stirring to mix. To this solution 10.0 ml. (9.55 g.,0.0336 moles) of tetraisopropyl titanate is added with good agitation.The ortho ester hydrolyzes immediately forming a white precipitate whichgradually redissolves forming a clear solution. This solution is thencoated on a grained aluminum sheet, dried, and sensitized with a diluteaqueous solution of diazo resin as in Example 5. When properly exposedand processed, as in Example 6, the titanyl fluoborate solution producesa suitable hydrophilic printing surface. Similar coatings are obtainedon the supports of Example 1.

Example 4.Preparation of a pertitanic acid coating compositionTetraisopropyl titanate is added to a dilute aqueous solution ofhydrogen peroxide in the same manner as the previous example. The whitehydrolysis product rapidly turns yellow and gradually dissolves toproduce a clear yellow solution. A particularly useful composition forapplication as in Example 1 contains 0.045 mole per liter of titaniumand 0.307 mole per liter of hydrogen peroxide. The hydrophilic characterof the surface obtained is enhanced by drying at an elevatedtemperature. Similar coatings are obtained on the supports of Example 1.

Example 5.-Diazo resin A diazo resin is prepared by mixing 34 gramsp-diazo diphenyl amine sulfate salt with 135 grams concentrated sulfuricacid which has been cooled to a temperature of 10 C. The mixture isagitated while the temperature is maintained at less than 3 C. while3.25 grams paraformaldehyde, and 6.05 grams anhydrous cadmium chlorideare added. The viscosity increases over a period of approximatelyone-half hour and the mixture becomes homogenous. The mixture is thenpoured over 150 grams of ice and stirred until the ice melts, the yellowprecipitate is filtered, redissolved in water and reprecipitated intotwo liters of isopropyl alcohol, filtered and dried under a vacuum inthe dark. Twenty-eight grams are obtained. This resin is a stabilizeddiazo resin.

Example 6 The treated, grained aluminum of Examples 1 and 2 is thensensitized by immersing in a dilute 2%, aqueous solution of diazo resin,passed between two rubber rolls to remove the excess and dried. Whenexposed at approximately 24 inches through a negative with a highintensity 220 volt carbon arc in a NuArc Printer, the exposed portionsare hardened.

The unexposed portions of the diazo resin are removed by washing withwater. The image is then lacquered with a commercially available imagelacquer.

The plate is then put on the lithographic printing press and produces90,000 satisfactory copies. Presensitized plates prepared according tothis example are found to have a shelf life for more than two years.

Example 7.Preparation of a preferred diazo resin sensitizer An 800 ml.beaker is equipped with a mechanically driven propeller type stirrer andexternal cooling is provided. To the reaction vessel is added 540 g.(5.35 moles) of 96 percent sulfuric acid followed by portion-wiseaddition of 138 g. (0.377 mole) of sensitizer DP (para diazo diphenylamine sulfate, obtained from Fairmount Chemi- Cal Co.) with stirring at25 to 35 C. until solution is complete. The mixture is then cooled andmaintained at 0 C. during the gradual addition of 100 ml. (0.592 mole)of 40 percent fiuoboric acid followed by the addition of 13.0 g. (0.432mole) paraformaldehyde with vigorous agitation to provide rapid anduniform dispersion of the paraformaldehyde. An additional 100 ml. (0.592mole) 40 percent fiuoboric acid is then added. The resultant mixture isnow deep red in color whereas prior to the initial addition of fiuoboricacid the solution was brownish in color. The reactant mixture is stirredand maintained at 0 C. for a period of one hour and ten minuteswhereupon it is poured with good agitation into 800 g. ice containing210 ml. (1.24 moles) of 40% fiuoboric acid. The precipitate which formsis then filtered and collected. The moist cake is'then dissolved in 700ml. dimethyl formamide and refiltered. The clear filtrate is thenagitated during the addition of 220 g. (0.965 mole) of cadmium chloride(CdCl '2 /2H O) dissolved in 250 ml. water. The precipitate thus formedis filtered and collected. The moist cake is then added to 2 liters ofisopropyl alcohol and stirred vigorously to produce a small uniformparticle size slurry. The slurry is filtered, collected and formed againin the same manner as above in 1 liter of diethyl ether. The slurry isthen filtered, collected and dried under vacuum at room temperature,care being taken to break up the moist cake to provide uniform drying.The yield of dry resin is 100 g. in the form of a light orange-yellowpowder.

Example 8.Preparation of a diazo resin sensitizer II In a 1500 ml. glassbeaker was placed 1040 g. of 96 percent sulfuric acid. The beaker wassuspended and equipped with a variable speed stirrer. The stirring acidwas cooled below 0 C. with a Dry Ice-acetone bath.

A 272 g. portion of Fairmount DP salt (Fairmount Chemical Co.) and 26 g.of paraformaldehyde were mixed together thoroughly in the dry state andthen added in portions to the acid, keeping the temperature below 5 C.The addition took 10 minutes. Stirring was continued for minutes,keeping the temperature below 0 C.

The acid solution was poured over a mixture of 2200 g. of crushed iceand a solution of 1 lb. of cadmium chloride in 600 ml. of water withgood agitation. A 3 liter portion of isopropyl alcohol was added and theresultant slurry filtered. The precipitate was slurried in 4 liters ofwater and 3 moles (624 g.) of barium chloride added. The resultantprecipitate was filtered off and subsequently extracted twice with threeliter portions of 0.75 M HF solution and a third time with 2 liters ofdistilled water. The filtrates were combined and a solution of 1 lb. ofcadmium chloride in 400 ml. added. Then 8 liters of isopropyl alcoholwere added and the slurry filtered. The

product was dried under vacuum at room temperature. The yield was 286 g.

Example 9 The treated grained aluminum of Examples 1 and 2 is sensitizedby coating with light sensitive polymers using the whirler coatingtechnique. Kodak Photo Resist yields a clean appearing image. Wheninked, 50 press copies are obtained on the lithographic press. KodakMetal Etch Resist is developed by tray development followed by waterwash-off and compressed air dried down to yield a robust, cleanappearing image. The image is resistant to prolonged rubbing. Lightsensitive compositions of the type described in US. Patent 2,948,610 areswab developed with 0.5% sodium carbonate to yield adherent,inkreceptive images. Azoplate Positop developed with Positop developeryields adherent robust images which show good press life. Lightsensitive polycarbonate resins of the type described in US. Patent3,043,802 are tray developed to yield clean, ink-receptive images. Anegative working wash-off light sensitive silver halide emulsion istransferred to the treated surface from the strippable support. Afteractivation, the untanned gelatin is washed off.

A light sensitive silver halide emulsion comprising the first gelatinlayer containing an oxidizing developer and a second layer containinglight sensitive silver halide is coated on the treated support. Asatisfactory lithographic plate is obtained after activation and inkingof the surface.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

We claim:

1. A coating composition for providing a hydrophilic layer saidcomposition comprising an aqueous solution having a pH of about 1 toabout 5 and containing the complex residues resulting from thedissolution of an alkyl titanate wherein the alkyl group contains 2-5carbon atoms and at least sufficient solubilizing compound selected fromthe class consisting of fluosilicic acid, fluoboric acid, hydrogenperoxide, a mixture of hydrogen peroxide and at least one of said acids,and a mixture of hydrogen peroxide and phosphoric acid to maintainaqueous solution.

2. A coating composition as in claim 1 for providing a hydrophilicsurface comprising an aqueous solution of a complex of an alkyl titanateand fluosilicic acid in molar ratio from about 1:1 to about 1:5.

3. A coating composition as in claim 1 for providing a hydrophilicsurface comprising an aqueous solution of a complex of an alkyl titanateand fluoboric acid in molar ratio of about 1:2 to about 1:7.

4. A coating composition as in claim 1 for providing a hydrophilicsurface comprising an aqueous solution of a complex of an alkyl titanateand hydrogen peroxide in molar ratio of about 1 to about 6.8-10.7.

5. A coating composition as in claim 1 for providing a hydrophilicsurface comprising an aqueous solution of a complex of an :alkyltitanate, hydrogen peroxide, and phosphoric acid wherein the molarratios vary from about 6.8-107 moles of hydrogen peroxide and 2.3-7moles phosphoric acid per mole titanate.

References Cited UNITED STATES PATENTS 3,159,613 12/1964 Vandenberg260-91.l 3,028,297 4/ 1962 Lagally 106299 3,002,854 9/ 1961 Brill260-4295 2,118,916 5/ 1938 Drucker 23-202 OTHER REFERENCES ChemicalAbstract 18,419 P, P. Viallet, 1961 copy in Chemical Library.

JULIUS FROME, Primary Examiner.

THEODORE MORRIS, Assistant Examiner.

U.S. CI. X.R. 96--33; 117-127

